I believe flexible PVC gives you less head lost from your return pump than elbows and 45 degree elbow. Eventless, another mentality of people would rather go with hard PVC all around for an ease of mind with potential leaks.
I used all flex tubing on the 125. I'm okay with it but I'll be using PVC on the new build. I will be using flex tubing to PVC on the return of the new build, simply because the pump will have to be removed periodically, and it just seems more convenient when the time comes to remove the return pump.
The better choice is obvious but they both work well. I wouldn't think far into it, just make sure everything is secured. You should be fine which ever way you decide to go. You're likely going to upgrade in a few years anyways.